The present invention relates to absorption refrigeration systems. More particularly, the present invention relates to absorbers for absorption refrigeration systems.
There are many different kinds of absorbers for absorption refrigeration systems. For example, an absorber may comprise a relatively large, closed vessel with baffle plates mounted therein to provide a tortuous passageway for refrigerant vapor and absorbent solution flowing in the absorber. The refrigerant vapor and the absorbent solution may be admitted at opposite ends of the closed vessel to provide a type of counterflow in the vessel wherein the flow streams of the vapor and the solution are randomly directed relative to each other. This kind of absorber is usually cooled by passing a cooling fluid through tubing located inside the absorber vessel.
In certain situations, it is desirable to provide an air-cooled absorber comprised of vertical tubes in which absorbent solution and refrigerant vapor are brought into contact by parallel flow streams of these fluids flowing inside each tube. Usually, the absorbent solution and the refrigerant vapor are supplied to the tops of the tubes and flow down to the bottoms of the tubes. The absorber is cooled by circulating cool air over the outside surfaces of the absorber tubes. However, in general, these conventional vertical tube absorbers do not operate as efficiently as possible. For example, it has been observed that weak absorbent solution produced by these absorbers does not always contain as much refrigerant as theoretically possible thus indicating that the performance of the absorber can be improved. Also, from a theoretical thermodynamic viewpoint, these parallel flow vertical tube absorbers have a relatively large thermodynamic driving force at the top of the absorber, where relatively strong absorbent solution is in contact with relatively high pressure refrigerant vapor, and a relatively small thermodynamic driving force at the bottom of the absorber, where relatively weak absorbent solution is in contact with relatively low pressure refrigerant vapor. This indicates that maximum performance of the absorber is not being obtained along the entire length of each of the absorber tubes since most of the absorption will occur at the top of the absorber tubes where the large driving force is present, and relatively little absorption will occur at the bottom of the absorber tubes where the relatively small driving force is present.
Also, parallel flow vertical tube absorbers present problems with respect to purging of non-condensibles which are usually purged from the bottom of the absorber where the relatively weak absorbent solution is collected. Non-condensibles have a tendency to flow up into the tubes of the absorber and not all of the non-condensibles can be purged from the bottom of the absorber.